* ricksbasseyetus wrote, On 5/15/2007 11:51 PM:
i own a 1988 winners boat and it has 5.7 ltr 350 small block chevrolet with
an alpha one stern drive and it overheats . the engine is new and the
outdrive has been gone through by a cert. Mercruiser tch. i have replaced
waterpump, impeller,gauge,some hoses and have went as far as to take out the
engine and outdrive to reinspect all the hard work we have done just to have
an good runnin boat 2 enjoy Lake Erie with . i'm about at the point and takin
revenge out on my wonderful craft because i'm lost for answer so PLEASE HELP .
.. stranded and overheatin in the middle of Lake Erie and need either a tow
or a ___________ ..... lets put are heads together and try to solve my
dilema!!!!!!!!!!


My experience is with smaller sailboat diesels, so it may not apply
here. However, I've seen two causes of overheating that can go
undiagnosed. One is a air lock in the line, in particular a water
heater line which leads up from the engine, thus making it hard to
completely fill the lines.

The other situation is a problem in the heat exchanger. If it is
partially clogged, it will work fine at lower loads, but overheat when
the load goes beyond its ability to remove heat. Unless you can
measure the heat content of the waste water, there is not way to
determine this is the problem without looking inside.

In my case, I had a bit of eel grass that clogged several of the
internal HE pipes. Once figured out, it was easy to deal with. I was
reading yesterday about a case where Yanmar 75 hp engines had heat
exchangers that had been tested in manufacturing with a bad solution
that left a coating on the inside that reduced efficiency. The
problem had plagued the owner for several years until discovered a few
weeks ago.